1. Field of the Invention
The present invention relates generally to thermosetting compositions that contain copolymers of vinyl monomers. More specifically, the present invention is directed to thermosetting compositions that contain functional copolymers containing isobutylene type monomers.
2. Description of Related Art
Reducing the environmental impact of coating compositions, in particular that associated with emissions into the air of volatile organics during their use, has been an area of ongoing investigation and development in recent years. Accordingly, interest in high solids liquid and powder coatings has been increasing due, in part, to their inherently low volatile organic content (VOC), which significantly reduces air emissions during the application process. While both thermoplastic and thermoset coating compositions are commercially available, thermoset coatings are typically more desirable because of their superior physical properties, e.g., hardness and solvent resistance.
Low VOC coatings are particularly desirable in the automotive original equipment manufacture (OEM) market due to the relatively large volume of coatings that are used. However, in addition to the requirement of low VOC levels, automotive manufacturers have very strict performance requirements of the coatings that are used. For example, automotive OEM clear top coats are typically required to have a combination of good exterior durability, acid etch and water spot resistance, and excellent gloss and appearance. While liquid top coats containing, for example, capped polyisocyanate and polyol components, can provide such properties, they have the undesirable drawback of higher VOC levels relative to higher solids liquid coatings or powder coatings, which have essentially zero VOC levels.
Coating compositions containing polyol and capped polyisocyanate components (xe2x80x9cisocyanate cured coatingsxe2x80x9d) are known and have been developed for use in a number of applications, such as-industrial and automotive OEM topcoats. Such isocyanate cured coating compositions are described in, for example, U.S. Pat. Nos. 4,997,900, 5,439,896, 5,508,337, 5,554,692, and 5,777,061. However, their use has been limited due to deficiencies in, for example, flow, appearance and storage stability. Isocyanate cured coating compositions typically include a crosslinker having two or more capped isocyanate groups, e.g., a trimer of 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane capped with e-caprolactam, and a hydroxy functional polymer, e.g., an acrylic copolymer prepared in part from a hydroxyalkyl acrylate and/or methacrylate.
Electrodeposition as a coating application method involves deposition of a film-forming composition onto a conductive substrate under the influence of an applied electrical potential. Electrodeposition has become increasingly important in the coatings industry because, by comparison with non-electrophoretic coating means, electrodeposition offers increased paint utilization, improved corrosion protection, and low environmental contamination.
Initially, electrodeposition was conducted with the workpiece being coated serving as the anode. This was familiarly referred to as anionic electrodeposition. However, in 1972, cationic electrodeposition was introduced commercially. Since that time, cationic electrodeposition has steadily gained in popularity and today is by far the most prevalent method of electrodeposition. Throughout the world, more than 80 percent of all motor vehicles produced are given a primer coating by cationic electrodeposition.
Electrodepositable coating compositions comprising active hydrogen-containing polymers which contain onium salt groups are known and have been developed for use, inter alia, in electrodepositable automotive OEM primer coatings. Such electrodepositable coating compositions typically comprise a crosslinking agent having at least two functional groups that are reactive with active hydrogen groups, and an active hydrogen-containing polymer which contains onium salt groups.
Functional polymers used in liquid, powder, and electrodepositable coating compositions are typically random copolymers that include functional group-containing acrylic and/or methacrylic monomers. Such a functional copolymer will contain a mixture of polymer molecules having varying individual functional equivalent weights and polymer chain structures. In such a copolymer, the functional groups are located randomly along the polymer chain. Moreover, the number of functional groups is not divided equally among the polymer molecules, such that some polymer molecules may actually be free of functionality.
In a thermosetting composition, the formation of a three-dimensional crosslinked network is dependent on the functional equivalent weight as well as the architecture of the individual polymer molecules that comprise it. Polymer molecules having little or no reactive functionality (or having functional groups that are unlikely to participate in crosslinking reactions due to their locations along the polymer chain) will contribute little or nothing to the formation of the three-dimensional crosslinked network, resulting in decreased crosslink density and less than optimum physical properties of the finally formed thermoset coating.
Many patents express the potential for using isobutylene-containing polymers in coating compositions. For example, U.S. Pat. No. 6,114,489 to Vicari et al. discloses a coating composition that includes a functional acrylic resin binder; a co-reactant capable of reacting with the functionality of the acrylic binder; a degasser; and a hyperbranched polyester flow and leveling agent. Isobutylene is suggested as a potential co-monomer for use in the acrylic binder as part of a long list of monomers. U.S. Pat. No. 5,552,487 to Clark et al. discloses powder coating compositions that include a copolymer having a reactive functionality and a suitable crosslinking agent capable of reaction with the reactive functionality of the copolymer. The copolymer is a made by copolymerizing functional monomers with other monomers, isobutylene being one among many listed as potential co-monomers. Although only two are referenced herein, of the many patents that express the possibility of using isobutylene-type co-monomers, none actually shows or discloses a working example of such a copolymer.
The fact that no examples of isobutylene-type monomer-containing copolymers in coating compositions can be found is most likely due to the generally non-reactive nature of isobutylene with acrylic and methacrylic monomers. Reactivity ratios for monomers can be calculated using the Alfrey-Price Q-e values (Robert Z. Greenley, Polymer Handbook, Fourth Edition, Brandrup, Immergut and Gulke, editors, Wiley and Sons, New York, N.Y., pp. 309-319 (1999)). The calculations may be carried out using the formulas I and II:
r1=(Q1/Q2)exp{xe2x88x92e1(e1xe2x88x92e2)}xe2x80x83xe2x80x83I
r2=(Q2/Q1)exp{xe2x88x92e2(e2xe2x88x92e1)}xe2x80x83xe2x80x83II
where r1 and r2 are the respective reactivity ratios of monomers 1 and 2, and Q1 and Q2 and e1 and e2 are the respective reactivity and polarity values for the respective monomers (Odian, Principals of Polymerization, 3rd Ed., Wiley-Interscience, New York, N.Y., Chapter 6, pp. 452-467 and 489-491 (1991)). Table 1 shows the calculated reactivity ratios of selected monomers with isobutylene:
As one skilled in the art of polymer chemistry can appreciate, when r1 is near zero and r2 has a value of 10 or more, monomer 2 is reactive toward both monomers and monomer 1 is reactive toward neither monomer. In other words, it is extremely difficult to prepare copolymers having significant amounts of both monomers. It is not surprising then that no examples can be found of coating compositions that include isobutylene-type monomer-containing copolymers, because the monomers do not tend to copolymerize.
In some cases, it is observed that monomers that do not readily homopolymerize are able to undergo rapid copolymerization reactions with each other. The most typical situation occurs when a strong electron donating monomer is mixed with a strong electron accepting monomer from which a regular alternating copolymer results after free radical initiation. Maleic anhydride is a widely used example of a strong electron accepting monomer. Styrene and vinyl ethers are typical examples of electron donating monomers. Systems, such as maleic anhydride-styrene, are known to form charge transfer complexes, which tend to place the monomers in alternating sequence prior to initiation. The application of the free radical initiator xe2x80x9ctiesxe2x80x9d the ordered monomers together to form an alternating copolymer (Cowie, Alternating Copolymers, Plenum, New York (1985)).
U.S. Pat. No. 2,378,629 to Hanford and U.S. Pat. No. 4,151,336 to Sackman et al. disclose that even when a moderately electron donating monomer, such as diisobutylene, is copolymerized with a strong electron acceptor monomer, such as maleic anhydride, an alternating copolymer results.
When a moderately electron donating monomer, such as isobutylene, is copolymerized with a moderately electron accepting monomer, such as an acrylic ester, poor incorporation of the electron donating monomer results. For example, free radical copolymerization of isobutylene (IB) and acrylic monomers has resulted in copolymers that contain at no more than 20-30% of IB and have low molecular weights because of the degradative chain transfer of IB. Examples of such copolymerizations of IB are disclosed by U.S. Pat. No. 2,411,599 to Sparks et al. and U.S. Pat. No. 2,531,196 to Brubaker et al.
Conjugated monomers, such as acrylic esters and acrylonitrile, have been shown to react with monomers such as propylene, isobutylene, and styrene, in the presence of Lewis acids, such as alkylaluminum halides, to give 1:1 alternating copolymers. The alternating copolymers were obtained when the concentration ratio of the Lewis acids to the acrylic esters was 0.9 and the concentration of IB was greater than the concentration of the acrylic esters (Hirooka et al, J. Polym. Sci. Polym. Chem., 11, 1281 (1973)). The metal halides vary the reactivity of the monomers by complexing with them. The electron donor monomer-electron acceptor monomer-metal halide complex leads to alternating copolymers (Mashita et al. Polymer, Vol. 36, No. 15, pp. 2973-2982, (1995)).
Copolymers of IB and methyl acrylate (MA) have also been obtained by using ethyl aluminum sesquichloride and 2-methyl pentanoyl peroxide as an initiating system. The resulting copolymer had an alternating structure, with either low (Kuntz et al, J. Polym. Sci. Polym. Chem., 16, 1747 (1978)) or high isotacticity in the presence of EtAlCl2 (10 molar % relative to MA). (Florjanczyk et al, Makromol. Chem., 183, 1081 (1982)).
Another method for making IB copolymers with acrylic esters involved alkyl boron halide, which was found to be much more active than alkyl aluminum halides in forming alternating copolymers. The resulting copolymer was an elastomer of high tensile strength and high thermal decomposition temperature with good oil resistance, especially at elevated temperatures (Mashita et al, Polymer, 36, 2983 (1995)).
U.S. Pat. No. 5,807,937 to Matyjaszewski et al. discloses a method of making alternating copolymers of isobutylene and methyl acrylate using an atom transfer radical polymerization (ATRP) process. The method requires the use of a suitable ATRP initiator, such as 1-phenylethyl bromide, and a suitable transition metal salt, such as CuBr with a ligand, such as 2,2xe2x80x2-bipyridyl to perform the complex redox initiation and propagation steps of the polymerization process.
Copolymers containing relatively high amounts (xe2x89xa730 mol %) of IB and acrylic esters have only been attained by free radical polymerization when Lewis acids or ATRP initiation systems have been employed. The polymer that results from such processes requires expensive and time consuming clean up to remove the transition metal salt and/or Lewis acid residues in order to make the polymer commercially useful.
Copolymer compositions that contain Lewis acids and/or transition metals intermingled with the copolymer can have a number of drawbacks when used commercially in coating compositions. First, some Lewis acids and transition metals are toxic and have adverse environmental effects if they are leached from the copolymer and enter the environment. Second, in coating applications the Lewis acids and transition metals may lead to poor color stability when the coating is exposed to UV light or simply cause the coating to discolor through other reactions or interactions. Further, the Lewis acids and transition metals may react with other ingredients in a coating formulation resulting in undesired properties, such as a shortened shelf-life for a given coating formulation.
It would be desirable to develop thermosetting compositions that comprise functional copolymers having a well-defined polymer chain structure. In particular, alternating copolymers containing isobutylene-type monomers that are substantially free of Lewis acids and transition metals would be desirable. Such compositions would have lower VOC levels due to lower viscosities and a combination of favorable performance properties particularly in coatings applications.
The present invention is directed to a liquid thermosetting composition that includes an ungelled copolymer composition and a crosslinking agent. The ungelled copolymer composition includes a functional group-containing copolymer that includes segments of alternating residues derived from a donor monomer composition comprising an acceptor monomer composition. The donor monomer composition includes one or a combination of isobutylene, diisobutylene, dipentene, and isoprenol and the acceptor monomer composition includes acrylic monomers and monomers containing functional groups. The ungelled copolymer composition is substantially free of transition metals and Lewis acids and the copolymer is substantially free of maleate-type monomer residues and fumarate-type monomer residues. The crosslinking agent has at least two functional groups that are reactive with the functional groups of the copolymer.
The present invention is also directed to a thermosetting composition that includes a co-reactable solid, particulate mixture of a reactant having at least two functional groups, and a copolymer composition. The copolymer composition includes a functional group-containing copolymer as described above. The copolymer composition is substantially free of transition metals and Lewis acids and the copolymer is substantially free of maleate-type monomer residues and fumarate-type monomer residues. The functional groups of the reactant are different from and reactive with the functional groups of the copolymer.
The present invention is further directed to a thermosetting composition that includes a resinous phase dispersed in an aqueous medium. The resinous phase includes an ungelled copolymer composition and a curing agent. The ungelled copolymer composition includes a functional group-containing copolymer that includes segments of alternating residues derived from a donor monomer composition comprising an acceptor monomer composition. The donor monomer composition includes one or a combination of isobutylene, diisobutylene, dipentene, and isoprenol and the acceptor monomer composition includes acrylic monomers and monomers containing one or more active hydrogen groups and residues from monomers containing salt groups. The copolymer composition is substantially free of transition metals and Lewis acids and the copolymer is substantially free of maleate-type monomer residues and fumarate-type monomer residues. The functional groups of the curing agent are different from and reactive with the active hydrogen groups of the copolymer.
The present invention is still further directed to a method of coating a substrate that includes applying a thermosetting composition to the substrate, coalescing the thermosetting composition to form a substantially continuous film, and curing the thermosetting composition. The thermosetting composition is the liquid thermosetting composition or the solid thermosetting composition described above. The present invention is directed to a substrate coated using the above described method.
The present invention is additionally directed to a method of electrocoating a conductive substrate serving as a cathode in an electrical circuit comprising the cathode and an anode. The cathode and anode are immersed in an aqueous electrocoating composition. The method includes passing electric current between the cathode and the anode to cause deposition of the electrocoating composition on the substrate as a substantially continuous film. The electrocoating composition includes the thermosetting composition that includes a resinous phase dispersed in an aqueous medium described above. The present invention is directed to a substrate coated using the above described method.
The present invention is also additionally directed to a multi-component composite coating composition that includes a base coat deposited from a pigmented film-forming composition and a transparent top coat applied over the base coat. The top coat may be applied using the above described method of applying the liquid thermosetting composition or the solid thermosetting composition of the present invention. The base coat may be applied using the above-described method of applying the present liquid thermosetting composition, the met hod of applying the present solid thermosetting composition and/or the present method of electrocoating a conductive substrate. The multi-component composite coating composition may have three coating layers where the first coat may be a primer coat including the present thermosetting composition applied using the present method of electrocoating a conductive substrate, the second coat is a base coat is as described above and the third coat is a top coat as described above.
Other than in the operating examples, or where otherwise indicated, all numbers or expressions referring to quantities of ingredients, reaction conditions, etc., used in the specification and claims are to be understood as modified in all instances by the term xe2x80x9cabout.xe2x80x9d Various numerical ranges are disclosed in this patent application. Because these ranges are continuous, they include every value between the minimum and maximum values. Unless expressly indicated otherwise, the various numerical ranges specified in this application are approximations.
As used herein, the term xe2x80x9ccopolymer compositionxe2x80x9d is meant to include a synthesized copolymer as well as residues from initiators, catalysts, and other elements attendant to the synthesis of the copolymer, but not covalently incorporated thereto. Such residues and other elements considered as part of the copolymer composition are typically mixed or co-mingled with the copolymer such that they tend to remain with the copolymer when it is transferred between vessels or between solvent or dispersion media.
As used herein, the term xe2x80x9csubstantially freexe2x80x9d is meant to indicate that a material is present as an incidental impurity. In other words, the material is not intentionally added to an indicated composition, but may be present at minor or inconsequential levels because it was carried over as an impurity as part of an intended composition component.
The terms xe2x80x9cdonor monomerxe2x80x9d and xe2x80x9cacceptor monomerxe2x80x9d are used throughout this application. With regard to the present invention, the term xe2x80x9cdonor monomerxe2x80x9d refers to monomers that have a polymerizable, ethylenically unsaturated group that has relatively high electron density in the ethylenic double bond, and the term xe2x80x9cacceptor monomerxe2x80x9d refers to monomers that have a polymerizable, ethylenically unsaturated group that has relatively low electron density in the ethylenic double bond. This concept has been quantified to an extent by the Alfrey-Price Q-e scheme (Robert Z. Greenley, Polymer Handbook, Fourth Edition, Brandrup, Immergut and Gulke, editors, Wiley and Sons, New York, N.Y., pp. 309-319 (1999)). All e values recited herein are those appearing in the Polymer Handbook unless otherwisw indicated.
In the Q-e scheme, Q reflects the reactivity of a monomer and e represents the polarity of a monomer, which indicates the electron density of a given monomer""s polymerizable, ethylenically unsaturated group. A positive value for e indicates that a monomer has a relatively low electron density and is an acceptor monomer, as is the case for maleic anhydride, which has an e value of 3.69. A low or negative value for e indicates that a monomer has a relatively high electron density and is a donor monomer, as is the case for vinyl ethyl ether, which has an e value of xe2x88x921.80.
As referred to herein, a strong acceptor monomer is meant to include those monomers with an e value greater than 2.0. The term xe2x80x9cmild acceptor monomerxe2x80x9d is meant to include those monomers with an e value greater than 0.5 up to and including those monomers with an e value of 2.0. Conversely, the term xe2x80x9cstrong donor monomerxe2x80x9d is meant to include those monomers with an e value of less than xe2x88x921.5, and the term xe2x80x9cmild donor monomerxe2x80x9d is meant to include those monomers with an e value of less than 0.5 to those with an e value of xe2x88x921.5.
The present invention is directed to a thermosetting composition that includes a copolymer composition that contains a functional group-containing copolymer having at least 30 mol %, in many cases at least 40 mol %, typically at least 50 mol %, in some cases at least 60 mol %, and in other cases at least 75 mol % of residues of the copolymer derived from alternating sequences of donor monomer-acceptor monomer pairs having the alternating monomer residue units of structure:
-[DM-AM]-
where DM represents a residue from a donor monomer and AM represents a residue from an acceptor monomer. The copolymer may be a 100% alternating copolymer of DM and AM. More particularly, at least 15 mol % of the copolymer comprises a donor monomer, which is an isobutylene-type monomer, having the following structure (I): 
where R1 is linear or branched C1 to C4 alkyl; R2 is one or more of methyl, linear, cyclic, or branched C1 to C20 alkyl, alkenyl, aryl, alkaryl, and aralkyl. Further, at least 15 mol % of the copolymer includes an acrylic monomer as an acceptor monomer. The group R2 may include one or more functional groups selected from hydroxy, epoxy, carboxylic acid, ether, carbamate, and amide.
Thermosetting compositions of the present invention often have a VOC content of less than 4 percent by weight, typically less than 3.5 percent by weight and many times less than 3 percent by weight.
Of note in the present copolymer is that the copolymer incorporates a substantial portion of alternating residues of a mild donor monomer as described by structure I and a mild acceptor monomer, which is an acrylic monomer. A non-limiting list of published e values for monomers that may be included as monomers described by structure I and acrylic monomers of the present invention are shown in Table 2.
The present copolymer composition is substantially free of maleate monomer residues and fumarate monomer residues, which typically have e values greater than 2.0. These types of multifunctional monomers provide too many functional groups to the copolymer. This can create problems, for example in coatings where a thermosetting composition may have a short shelf-life due to the overly functional nature of the copolymer.
Further, the present copolymer composition is substantially free of transition metals and Lewis acids which, as noted above, have been used in the prior art to make alternating copolymers of mild donor monomers and mild acceptor monomers. The present invention does not utilize transition metal or Lewis acid adjuncts in preparing the present copolymer composition, therefore, they need not be removed after polymerization and the resulting copolymer compositions will not suffer the drawbacks inherent in those that contain transition metals or Lewis acids.
Any suitable donor monomer may be used in the present invention. Suitable donor monomers that may be used include strong donor monomers and mild donor monomers. The present invention is particularly useful for preparing alternating copolymers where a mild donor molecule is used. The present copolymers will include a mild donor monomer described by structure I, such as isobutylene and diisobutylene, dipentene, and isoprenol, and may additionally include other suitable mild donor monomers. The mild donor monomer of structure I is present in the copolymer composition at a level of at least 15 mol %, in some cases at least 25 mol %, typically at least 30 mol % and in some cases at least 35 mol %. The mild donor monomer of structure I is present in the copolymer composition at a level of up to 50 mol %, in some cases up to 47.5 mol %, typically up to 45 mol %, and, in some cases, up to 40 mol %. The level of the mild donor monomer of structure I used is determined by the properties that are to be incorporated into the copolymer composition. Residues from the mild donor monomer of structure 1 may be present in the copolymer composition in any range of values inclusive of those stated above.
Suitable other donor monomers that may be used in the present invention include, but are not limited to, ethylene, butene, styrene, substituted styrenes, methyl styrene, substituted styrenes, vinyl ethers, vinyl esters, vinyl pyridines, divinyl benzene, vinyl naphthalene, and divinyl naphthalene. Vinyl esters include vinyl esters of carboxylic acids which include, but are not limited to, vinyl acetate, vinyl butyrate, vinyl 3,4-dimethoxybenzoate, and vinyl benzoate. The use of other donor monomers is optional, when other donor monomers are present, they are present at a level of at least 0.01 mol % of the copolymer composition, often at least 0.1 mol %, typically at least 1 mol %, and, in some cases, at least 2 mol %. The other donor monomers may be present at up to 25 mol %, in some cases up to 20 mol %, typically up to 10 mol %, and, in some cases, up to 5 mol %. The level of other donor monomers used is determined by the properties that are to be incorporated into the copolymer composition. Residues from the other donor monomers may be present in the copolymer composition in any range of values inclusive of those stated above.
The copolymer composition includes acceptor monomers as part of the alternating donor monomer-acceptor monomer units along the copolymer chain. Any suitable acceptor monomer may be used. Suitable acceptor monomers include strong acceptor monomers and mild acceptor monomers. A non-limiting class of suitable acceptor monomers are those described by the structure (II): 
where W is selected from the group consisting of xe2x80x94CN, xe2x80x94X, and xe2x80x94C(xe2x95x90O)xe2x80x94Y, wherein Y is selected from the group consisting of xe2x80x94NR32, xe2x80x94Oxe2x80x94R5xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94NR32, and xe2x80x94OR4, R3 is selected from the group consisting of H, linear or branched C1 to C20 alkyl, and linear or branched C1 to C20 alkylol, R4 is selected from the group consisting of H, poly(ethylene oxide), poly(propylene oxide), linear or branched C1 to C20 alkyl, alkylol, aryl and aralkyl, linear or branched C1 to C20 fluoroalkyl, fluoroaryl and fluoroaralkyl, a siloxane radical, a polysiloxane radical, an alkyl siloxane radical, an ethoxylated trimethylsilyl siloxane radical, and a propoxylated trimethylsilyl siloxane radical, R5 is a divalent linear or branched C1 to C20 alkyl linking group, and X is a halide.
A class of mild acceptor monomers that are included in the present copolymer composition are acrylic acceptor monomers. Suitable acrylic acceptor monomers include those described by structure (III): 
where Y is selected from the group consisting of xe2x80x94NR32, xe2x80x94Oxe2x80x94R5xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94NR32, and xe2x80x94OR4, R3 is selected from the group consisting of H, linear or branched C1 to C20 alkyl, and linear or branched C1 to C20 alkylol, R4 is selected from the group consisting of H, poly(ethylene oxide), poly(propylene oxide), linear or branched C1 to C20 alkyl, alkylol, aryl and aralkyl, linear or branched C1 to C20 fluoroalkyl, fluoroaryl and fluoroaralkyl, a siloxane radical, a polysiloxane radical, an alkyl siloxane radical, an ethoxylated trimethylsilyl siloxane radical, and a propoxylated trimethylsilyl siloxane radical, and R5 is a divalent linear or branched C1 to C20 alkyl linking group.
A particularly useful type of acrylic acceptor monomers are those described by structure III where Y includes at least one functional group of epoxy, oxirane, carboxylic acid, hydroxy, methylol, methylol ether, amide, oxazoline, aceto acetate, isocyanate, carbamate, primary amine, secondary amine salt, quaternized amine, thioether, sulfide, sulfonium salt, or phosphate.
Examples of suitable acceptor monomers include, but are not limited to, hydroxyethyl acrylate, hydroxypropyl acrylate, acrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, isobutyl acrylate, isobornyl acrylate, dimethylaminoethyl acrylate, acrylamide, perfluoro methyl ethyl acrylate, perfluoro ethyl ethyl acrylate, perfluoro butyl ethyl acrylate, trifluoromethyl benzyl acrylate, perfluoro alkyl ethyl, acryloxyalkyl terminated polydimethylsiloxane, acryloxyalkyl tris(trimethylsiloxy silane), and acryloxyalkyl trimethylsiloxy terminated polyethylene oxide, chlorotrifluoro ethylene, glycidyl acrylate, 2-ethylhexyl acrylate, and n-butoxy methyl acrylamide.
The acrylic acceptor monomers of structure III are present in the copolymer composition at a level of at least 15 mol %, in some cases at least 25 mol %, typically at least 30 mol %, and, in some cases, at least 35 mol %. The acrylic acceptor monomers of structure III are present in the copolymer composition at a level of up to 50 mol %, in some cases up to 47.5 mol %, typically up to 45 mol %, and, in some cases, up to 40 mol %. The level of the acrylic acceptor monomers of structure III used is determined by the properties that are to be incorporated into the copolymer composition. Residues from the acrylic acceptor monomers of structure III may be present in the copolymer composition in any range of values inclusive of those stated above.
Suitable other mild acceptor monomers that may be used in the present invention include, but are not limited to, acrylonitrile, methacrylonitrile, vinyl halides, crotonic acid, vinyl alkyl sulfonates, and acrolein. Vinyl halides include, but are not limited to, vinyl chloride and vinylidene fluoride. The use of other mild acceptor monomers is optional, when other mild acceptor monomers are present, they are present at a level of at least 0.01 mol % of the copolymer composition, often at least 0.1 mol %, typically at least 1 mol %, and, in some cases, at least 2 mol %. The other acceptor monomers may be present at up to 35 mol %, in some cases up to 25 mol %, typically up to 15 mol %, and, in some cases, up to 10 mol %. The level of other acceptor monomers used is determined by the properties that are to be incorporated into the copolymer composition. Residues from the other acceptor monomers may be present in the copolymer composition in any range of values inclusive of those stated above.
The present copolymer has a molecular weight of at least 250, in many cases at least 500, typically at least 1,000, and, in some cases, at least 2,000. The present copolymer may have a molecular weight of up to 1,000,000, in many cases up to 500,000, typically up to 100,000, and, in some cases, up to 50,000. Certain applications will require that the molecular weight of the present copolymer not exceed 30,000, in some cases not exceed 25,000, in other cases not exceed 20,000, and, in certain instances, not exceed 16,000. The molecular weight of the copolymer is selected based on the properties that are to be incorporated into the copolymer composition. The molecular weight of the copolymer may vary in any range of values inclusive of those stated above.
The polydispersity index (PDI) of the present copolymer is not always critical. The polydispersity index of the copolymer is usually less than 4, in many cases less than 3.5, typically less than 3.0, and, in some cases, less than 2.5. As used herein, and in the claims, xe2x80x9cpolydispersity indexxe2x80x9d is determined from the following equation: (weight average molecular weight (Mw)/number average molecular weight (Mn)). A monodisperse polymer has a PDI of 1.0. Further, as used herein, Mn and Mw are determined from gel permeation chromatography using polystyrene standards.
In an embodiment of the present copolymer composition, the alternating sequences of donor monomer-acceptor monomer pairs are residues have the alternating structure IV: 
where R1, R2, and W are defined as above. A particularly preferred embodiment is one wherein the monomer residues containing the group W are derived from one or more acrylic monomers, and the monomer residues containing the groups R1 and R2 are derived from one or a combination of diisobutylene, isobutylene, dipentene, and isoprenol. The copolymer compositions of the present invention may also include other polymerizable, ethylenically unsaturated monomers.
The copolymer composition of the present invention may have all of the incorporated monomer residues in an alternating architecture. A non-limiting example of a copolymer segment having 100% alternating architecture of diisobutylene (DIIB) and an acrylic monomer (Ac) is shown by structure V:
-Ac-DIIB-Ac-DIIB-Ac-DIIB-Ac-DIIB-Ac-DIIB-Ac-DIIB-Ac-xe2x80x83xe2x80x83(V)
However, in most instances, the present copolymer will contain alternating segments and random segments as shown by structure VI, a copolymer of DIIB, Ac and other monomers, M: 
Structure VI shows an embodiment of the present invention where the copolymer may include alternating segments as shown in the boxes and random segments as shown by the underlined segments.
The random segments of the copolymer may contain donor or acceptor monomer residues that have not been incorporated into the copolymer composition by way of an alternating architecture. The random segments of the copolymer composition may further include residues from other ethylenically unsaturated monomers. As recited herein, all references to polymer segments derived from alternating sequences of donor monomer-acceptor monomer pairs are meant to include segments of monomer residues such as those shown by the boxes in structure VI.
The other ethylenically unsaturated monomers include any suitable monomer not traditionally categorized as being an acceptor monomer or a donor monomer.
The other ethylenically unsaturated monomers, residue M of structure VI, is derived from at least one ethylenically unsaturated, radically polymerizable monomer. As used herein and in the claims, xe2x80x9cethylenically unsaturated, radically polymerizable monomerxe2x80x9d, and like terms, are meant to include vinyl monomers, allylic monomers, olefins, and other ethylenically unsaturated monomers that are radically polymerizable and not classified as donor monomers or acceptor monomers.
Classes of vinyl monomers from which M may be derived include, but are not limited to monomer residues derived from monomers of the general formula VII: 
where R11, R12, and R14 are independently selected from the group consisting of H, CF3, straight or branched alkyl of 1 to 20 carbon atoms, aryl, unsaturated straight or branched alkenyl or alkynyl of 2 to 10 carbon atoms, unsaturated straight or branched alkenyl of 2 to 6 carbon atoms substituted with a halogen, C3-C8 cycloalkyl, heterocyclyl and phenyl; R13 is selected from the group consisting of H, C1-C6 alkyl, COOR15, wherein R15 is selected from the group consisting of H, an alkali metal, a C1 to C6 alkyl group, glycidyl, and aryl.
Specific examples of other monomers, M, that may be used in the present invention include methacrylic monomers and allylic monomers. Residue M may be derived from at least one of alkyl methacrylate having from 1 to 20 carbon atoms in the alkyl group. Specific examples of alkyl methacrylates having from 1 to 20 carbon atoms in the alkyl group from which residue M may be derived include, but are not limited to, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, isobornyl methacrylate, cyclohexyl methacrylate, 3,3,5-trimethylcyclohexyl methacrylate, as well as functional methacrylates, such as hydroxyalkyl methacrylates, oxirane functional methacrylates, and carboxylic acid functional methacrylates.
Residue M may also be selected from monomers having more than one methacrylate group, for example, methacrylic anhydride and diethyleneglycol bis(methacrylate).
As used herein and in the claims, by xe2x80x9callylic monomer(s)xe2x80x9d what is meant is monomers containing substituted and/or unsubstituted allylic functionality, i.e., one or more radicals represented by the following general formula VIII,
H2Cxe2x95x90C(R10)xe2x80x94CH2xe2x80x94xe2x80x83xe2x80x83(VIII)
where R10 is hydrogen, halogen, or a C1 to C4 alkyl group. Most commonly, R10 is hydrogen or methyl and, consequently, general formula VII represents the unsubstituted (meth)allyl radical, which encompasses both allyl and methallyl radicals. Examples of allylic monomers include, but are not limited to, (meth)allyl alcohol; (meth)allyl ethers, such as methyl (meth)allyl ether; allyl esters of carboxylic acids, such as (meth)allyl acetate, (meth)allyl butyrate, (meth)allyl 3,4-dimethoxybenzoate, and (meth)allyl benzoate.
The present copolymer composition is prepared by a method including the steps of (a) providing a donor monomer composition comprising one or more donor monomers of structure I; (b) mixing an ethylenically unsaturated monomer composition comprising one or more acceptor monomers with (a) to form a total monomer composition substantially free of maleate- and fumarate-type monomers; and (c) polymerizing the total monomer composition in the presence of a free radical initiator in the substantial absence of transition metals and Lewis acids. In an embodiment of the present invention, the ethylenically unsaturated monomer composition includes monomers of structure III.
In an embodiment of the present method, the monomer of structure I is present at a molar excess based on the amount of acrylic acceptor monomer. Any amount of excess monomer of structure I may be used in the present invention in order to encourage the formation of the desired alternating architecture. The excess amount of monomer of structure I may be at least 10 mol %, in some cases up to 25 mol %, typically up to 50 mol %, and, in some cases, up to 100 mol % based on the amount of acrylic acceptor monomer. When the molar excess of monomer of structure I is too high, the process may not be economical on a commercial scale.
In a further embodiment of the present method, the acrylic acceptor monomer is present in an amount of at least 15 mol %, in some cases 17.5 mol %, typically at least 20 mol %, and, in some cases, 25 mol % of the total monomer composition. The acrylic acceptor monomer may further be present in an amount up to 50 mol %, in some cases up to 47.5 mol %, typically up to 45 mol %, and, in some cases, up to 40 mol % of the total monomer composition. The level of the acrylic acceptor monomers used is determined by the properties that are to be incorporated into the copolymer composition. The acrylic acceptor monomers may be present in the monomer composition in any range of values inclusive of those stated above.
The ethylenically unsaturated monomer composition of the present method may include other donor monomers as described above, as well as other monomers designated by M and described above. The use of other mild acceptor monomers is optional in the present method. When other mild acceptor monomers are present, they are present at a level of at least 0.01 mol % of the copolymer composition, often at least 0.1 mol %, typically at least 1 mol %, and, in some cases, at least 2 mol % of the total monomer composition. The other acceptor monomers may be present at up to 35 mol %, in some. cases up to 25 mol %, typically up to 15 mol %, and, in some cases, up to 10 mol % of the total monomer composition. The level of other acceptor monomers used herein is determined by the properties that are to be incorporated into the copolymer composition. Residues from the other acceptor monomers may be present in the copolymer composition in any range of values inclusive of those stated above.
The use of other monomers, M, is optional in the present method. When other monomers are present, they are present at a level of at least 0.01 mol % of the copolymer composition, often at least 0.1 mol %, typically at least 1 mol %, and, in some cases, at least 2 mol %. The other monomers may be present at up to 35 mol %, in some cases up to 25 mol %, typically up to 15 mol %, and, in some cases, up to 10 mol %. The level of other monomers used herein is determined by the properties that are to be incorporated into the copolymer composition. Residues from the other monomers, M, may be present in the copolymer composition in any range of values inclusive of those stated above.
In an embodiment of the present method, an excess of monomer of structure I is used and the unreacted monomer of structure I is removed from the resulting copolymer composition by evaporation. The removal of unreacted monomer is typically facilitated by the application of a vacuum to the reaction vessel.
Any suitable free radical initiator may be used in the present invention. Examples of suitable free radical initiators include, but are not limited to, thermal free radical initiators, photo-initiators, and redox initiators. Examples of suitable thermal free radical initiators include, but are not limited to, peroxide compounds, azo compounds, and persulfate compounds.
Examples of suitable peroxide compound initiators include, but are not limited to, hydrogen peroxide, methyl ethyl ketone peroxides, benzoyl peroxides, di-t-butyl peroxide, di-t-amyl peroxide, dicumyl peroxide, diacyl peroxides, decanoyl peroxides, lauroyl peroxides, peroxydicarbonates, peroxyesters, dialkyl peroxides, hydroperoxides, peroxyketals, and mixtures thereof.
Examples of suitable azo compounds include, but are not limited to, 4-4xe2x80x2-azobis(4-cyanovaleric acid), 1xe2x80x2-1xe2x80x2-azobiscyclohexanecarbonitrile), 2-2xe2x80x2-azobisisobutyronitrile, 2-2xe2x80x2-azobis(2-methylpropionamidine) dihydrochloride, 2-2xe2x80x2-azobis(2-methylbutyronitrile), 2-2xe2x80x2-azobis(propionitrile), 2-2xe2x80x2-azobis(2,4-dimethylvaleronitrile), 2-2xe2x80x2-azobis(valeronitrile), 2,2xe2x80x2-azobis[2-methyl-N-(2-hydroxyethyl)propionamide], 4,4xe2x80x2-azobis(4-cyanopentanoic acid), 2,2xe2x80x2-azobis(N,Nxe2x80x2-dimethyleneisobutyramidine), 2,2xe2x80x2-azobis(2-amidinopropane) dihydrochloride, 2,2xe2x80x2-azobis(N,Nxe2x80x2-dimethyleneisobutyramidine) dihydrochloride, and 2-(carbamoylazo)-isobutyronitrile.
In an embodiment of the present invention, the ethylenically unsaturated monomer composition and the free radical polymerization initiator are separately and simultaneously added to and mixed with the donor monomer composition. The ethylenically unsaturated monomer composition and the free radical polymerization initiator may be added to the donor monomer composition over a period of at least 15 minutes, in some cases at least 20 minutes, typically at least 30 minutes, and, in some cases, at least 1 hour. The ethylenically unsaturated monomer composition and the free radical polymerization initiator may further be added to the donor monomer composition over a period of up to 24 hours, in some case up to 18 hours, typically up to 12 hours, and, in some cases, up to 8 hours. The time for adding the ethylenically unsaturated monomer must be sufficient to maintain a suitable excess of donor monomer of structure I over unreacted acrylic acceptor monomer to encourage the formation of donor monomer-acceptor monomer alternating segments. The addition time is not so long as to render the process economically unfeasible on a commercial scale. The addition time may vary in any range of values inclusive of those stated above.
After mixing or during addition and mixing, polymerization of the monomers takes place. The present polymerization method can be run at any suitable temperature. Suitable temperature for the present method may be ambient, at least 50xc2x0 C., in many cases at least 60xc2x0 C., typically at least 75xc2x0 C., and, in some cases, at least 100xc2x0 C. Suitable temperature for the present method may further be described as being up to 300xc2x0 C., in many cases up to 275xc2x0 C., typically up to 250xc2x0 C., and, in some cases, up to 225xc2x0 C. The temperature is typically high enough to encourage good reactivity from the monomers and initiators employed. However, the volatility of the monomers and corresponding partial pressures create a practical upper limit on temperature determined by the pressure rating of the reaction vessel. The polymerization temperature may vary in any range of values inclusive of those stated above.
The present polymerization method can be run at any suitable pressure. A suitable pressure for the present method may be ambient, at least 1 psi, in many cases at least 5 psi, typically at least 15 psi, and, in some cases, at least 20 psi. Suitable pressures for the present method may further be described as being up to 200 psi, in many cases up to 175 psi, typically up to 150 psi, and, in some cases, up to 125 psi. The pressure is typically high enough to maintain the monomers and initiators in a liquid phase. The pressures employed have a practical upper limit based on the pressure rating of the reaction vessel employed. The pressure during polymerization temperature may vary in any range of values inclusive of those stated above.
The copolymer that results from the present method may be utilized as a starting material for the preparation of other polymers by using functional group transformations by methods known in the art. Functional groups that can be introduced by these methods are epoxy, carboxylic acid, hydroxy, amide, oxazoline, acetoacetate, isocyanate, carbamate, amine, amine salt, quaternary ammonium, thioether, sulfide, sulfonium and phosphate.
For example, a copolymer of the present method comprising methyl acrylate will contain carbomethoxy groups. The carbomethoxy groups can be hydrolyzed to carboxyl groups or transesterified with an alcohol to form the corresponding ester of the alcohol. Using ammonia, the aforementioned methyl acrylate copolymer can be converted to an amide, or, using a primary or secondary amine, can be converted to the corresponding N-substituted amide. Similarly, using a diamine such as ethylene diamine, one can convert the aforementioned copolymer of the present method to an N-aminoethylamide, or, with ethanolamine, to an N-hydroxyethylamide. The N-aminoethylamide functionality can be further converted to an oxazoline by dehydration. The N-aminoethylamide can be further reacted with a carbonate such as propylene carbonate to produce the corresponding urethane functional copolymer. These transformations can be carried out to convert all of the carbomethoxy groups or can be carried out in part, leaving some of the carbomethoxy groups intact.
Epoxy groups can be introduced into the copolymer of the present method directly by using glycidyl acrylate in the copolymer preparation or indirectly by functional group transformation. One example of an indirect method is to oxidize residual unsaturation in the copolymer to epoxy groups using a peracid such as peroxyacetic acid. Alternatively one can prepare a carboxyl-functional copolymer by hydrolysis as described above, treat the carboxyl-functional copolymer with epichlorohydrin then alkali to produce the epoxy functional copolymer. These transformations can also be carried out exhaustively or in part. The resulting epoxy-functional copolymer can be further reacted with the appropriate active hydrogen containing reagents to form alcohols, amines or sulfides.
Hydroxyl groups can be introduced directly using a hydroxyl-functional monomer such as hydroxyethyl acrylate in the copolymer of the present method, or they can be introduced by functional group transformation. By treating the carboxyl-functional copolymer described above with an epoxy one can produce a hydroxyl functional polymer. Suitable epoxies include, but are not limited to, ethylene oxide, propylene oxide, butylene oxide and glycidyl neodecanoate.
The above-described hydroxyl functional copolymers can be further reacted to form other copolymers. For example, a copolymer containing hydroxyethyl groups can be treated with a carbamylating agent, such as methyl carbamate, to produce the corresponding carbamate functional copolymer. With diketene or t-butyl acetoacetate the hydroxyl groups can also be converted to acetoacetate esters.
Isocyanate functional copolymers can also be produced. Copolymers of the present method, which contain 2 or more hydroxyl groups, can be treated with a diisocyanate such as isophoronediisocyanate to produce isocyanate-functional polymers. Primary amine functional copolymers, described above, can be phosgenated to produce isocyanate functionality.
Ionic functionality can be incorporated into the copolymer of the present method by any means known in the art. Carboxylate groups can be introduced by hydrolysis of ester groups in the copolymer followed by reaction with base. Amine salts can be introduced by preparing the present copolymer with an amine functional acrylate, such as dimethylaminoethyl acrylate, followed by protonation of the amino groups with an acid. Amine salts can also be introduced by reacting a glycidyl functional copolymer with ammonia or an active hydrogen containing amine followed by protonation with acid. Quaternary amine functional groups or ternary sulfonium groups can be introduced into the copolymer by treating an epoxy functional copolymer of the present method with a tertiary amine or sulfide, respectively, in the presence of a protic acid.
A particular embodiment of the present invention is directed to a liquid thermosetting composition that includes an ungelled copolymer composition, that is the copolymer composition containing a functional group-containing copolymer of the present invention and a crosslinking agent having at least two functional groups that are reactive with the functional groups of the copolymer.
In the liquid thermosetting composition, the functional groups in the copolymer are any suitable functional groups. Suitable functional groups include, but are not limited to, epoxy or oxirane, carboxylic acid, hydroxy, amide, oxazoline, aceto acetate, isocyanate, methylol, methylol ether, and carbamate. The crosslinking agent will have suitable functional groups that will react with the functional groups in the copolymer. Suitable functional groups for the crosslinking agent include, but are not limited to, epoxy or oxirane, carboxylic acid, hydroxy, polyol, isocyanate, capped isocyanate, amine, methylol, methylol ether, aminoplast and beta-hydroxyalkylamide.
The functional copolymer will typically have a functional equivalent weight of from 100 to 5,000 grams/equivalent. The equivalent ratio of functional groups of the crosslinking agent to functional equivalents in the functional copolymer is typically within the range of 1:3 to 3:1. The crosslinking agent is present in the liquid thermosetting composition in an amount of from 1 to 45 percent by weight, based on total weight of resin solids, and the functional copolymer is present in an amount of from 55 to 99 percent by weight, based on total weight of resin solids.
A non-limiting example of the present liquid thermosetting composition is one where the functional group of the copolymer is hydroxy and the functional group of the crosslinking agent is a capped polyisocyanate, where the capping group of the capped polyisocyanate crosslinking agent is one or more of hydroxy functional compounds, 1H-azoles, lactams, ketoximes, and mixtures thereof. The capping group may be phenol, p-hydroxy methylbenzoate, 1H-1,2,4-triazole, 1H-2,5-dimethyl pyrazole, 2-propanone oxime, 2-butanone oxime, cyclohexanone oxime, e-caprolactam, or mixtures thereof. The polyisocyanate of the capped polyisocyanate crosslinking agent is one or more of 1,6-hexamethylene diisocyanate, cyclohexane diisocyanate, xcex1,xcex1xe2x80x2-xylylene diisocyanate, xcex1,xcex1,xcex1xe2x80x2,xcex1xe2x80x2-tetramethylxylylene diisocyanate, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane, diisocyanato-dicyclohexylmethane, dimers of the polyisocyanates, or trimers of the polyisocyanates.
When the copolymer has hydroxy functionality, it will typically have a hydroxy equivalent weight of from 100 to 10,000 grams/equivalent. The equivalent ratio of isocyanate equivalents in the capped polyisocyanate crosslinking agent to hydroxy equivalents in the hydroxy functional copolymer is typically within the range of 1:3 to 3:1. In this embodiment, the capped polyisocyanate crosslinking agent is present in the liquid thermosetting composition in an amount of from 1 to 45 percent by weight, based on total weight of resin solids, and the hydroxy functional copolymer is present in an amount of from 55 to 99 percent by weight, based on total weight of resin solids.
Another non-limiting example of the present liquid thermosetting composition is one where the copolymer has epoxy functional groups and the crosslinking agent is a carboxylic acid functional compound having from 4 to 20 carbon atoms. The carboxylic acid crosslinking agent may be one or more of dodecanedioic acid, azelaic acid, adipic acid, 1,6-hexanedioic acid, succinic acid, pimelic acid, sebacic acid, maleic acid, citric acid, itaconic acid, or aconitic acid.
A further non-limiting example of the present liquid thermosetting composition is one where the copolymer has carboxylic acid functional groups and the crosslinking agent is a beta-hydroxyalkylamide compound. The liquid thermosetting composition may further include a second polycarboxylic acid functional material selected from the group consisting of C4 to C20 aliphatic carboxylic acids, polymeric polyanhydrides, polyesters, polyurethanes and mixtures thereof. The beta-hydroxyalkylamide may be represented by the following structure IX: 
where R24 is H or C1-C5 alkyl; R25 is H, C1-C5 alkyl structure X: 
for which R24 is as described above, E is a chemical bond or monovalent or polyvalent organic radical derived from saturated, unsaturated, or aromatic hydrocarbon radicals including substituted hydrocarbon radicals containing from 2 to 20 carbon atoms, m is 1 or 2, n is from 0 to 2, and m+n is at least 2.
The liquid thermosetting composition of the present invention is preferably used as a film-forming (coating) composition and may contain adjunct ingredients conventionally used in such compositions. Optional ingredients such as, for example, plasticizers, surfactants, thixotropic agents, anti-gassing agents, organic cosolvents, flow controllers, anti-oxidants, UV light absorbers and similar additives conventional in the art may be included in the composition. These ingredients are typically present at up to about 40% by weight based on the total weight of resin solids.
The liquid thermosetting composition of the present invention may be waterborne, but is usually solventborne. Suitable solvent carriers include the various esters, ethers, and aromatic solvents, including mixtures thereof, that are known in the art of coating formulation. The composition typically has a total solids content of about 40 to about 80 percent by weight. The liquid thermosetting compositions of the present invention will often have a VOC content of less than 4 percent by weight, typically less than 3.5 percent by weight and many times less than 3 percent by weight.
The liquid thermosetting composition of the present invention may contain color pigments conventionally used in surface coatings and may be used as a monocoat; that is, a pigmented coating. Suitable color pigments include, for example, inorganic pigments such as titanium dioxide, iron oxides, chromium oxide, lead chromate, and carbon black, and organic pigments such as phthalocyanine blue and phthalocyanine green. Mixtures of the above mentioned pigments may also be used. Suitable metallic pigments include, in particular, aluminum flake, copper bronze flake, and metal oxide coated mica, nickel flakes, tin flakes, and mixtures thereof.
In general, the pigment is incorporated into the coating composition in amounts up to about 80 percent by weight based on the total weight of coating solids. The metallic pigment is employed in amounts of about 0.5 to about 25 percent by weight based on the total weight of coating solids.
In another embodiment, the present thermosetting composition is a co-reactable solid, particulate mixture, or powder of a reactant having at least two functional groups and the present functional group-containing copolymer composition. In the powder thermosetting composition, the reactant may have functional groups selected from epoxy or oxirane, carboxylic acid, hydroxy, polyol, isocyanate, capped isocyanate, amine, aminoplast, methylol, methylol ether, and beta-hydroxyalkylamide. The functional groups of the copolymer may be one or more of epoxy or oxirane, carboxylic acid, hydroxy, amide, oxazoline, aceto acetate, isocyanate, methylol, methylol ether, and carbamate. The functional groups of the reactant will react with the functional groups in the copolymer.
The functional copolymer typically has a functional group equivalent weight of from 100 to 5,000 grams/equivalent and the equivalent ratio of reactant functional groups to functional copolymer functional groups is within the range of 1:3 to 3:1. Typically, the reactant is present in an amount of from 1 to 45 percent by weight, based on total weight of resin solids, and the functional copolymer is present in an amount of from 55 to 99 percent by weight, based on total weight of resin solids.
In an embodiment of the present powder thermosetting composition the functional groups of the copolymer are hydroxy functional groups and the reactant is a capped polyisocyanate crosslinking agent. In this embodiment, the capping group of the capped polyisocyanate crosslinking agent is one or more of hydroxy functional compounds, 1H-azoles, lactams, and ketoximes. The capping group is one or more of phenol, p-hydroxy methylbenzoate, 1H-1,2,4-triazole, 1H-2,5-dimethyl pyrazole, 2-propanone oxime, 2-butanone oxime, cyclohexanone oxime, and e-caprolactam. The polyisocyanate of the capped polyisocyanate crosslinking agent is one or more of 1,6-hexamethylene diisocyanate, cyclohexane diisocyanate, xcex1,xcex1xe2x80x2-xylylene diisocyanate, xcex1,xcex1,xcex1xe2x80x2,xcex1xe2x80x2-tetramethylxylylene diisocyanate, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane, 2,4,4-trimethyl hexamethylene diisocyanate, 2,2,4-trimethyl hexamethylene diisocyanate, diisocyanato-dicyclohexylmethane, dimers of said polyisocyanates, and trimers of the polyisocyanates.
The hydroxy functional copolymer typically has a hydroxy equivalent weight of from 100 to 10,000 grams/equivalent and the equivalent ratio of isocyanate equivalents in the capped polyisocyanate crosslinking agent to hydroxy equivalents in the hydroxy functional copolymer is within the range of 1:3 to 3:1. Typically, the capped polyisocyanate crosslinking agent is present in an amount of from 1 to 45 percent by weight, based on total weight of resin solids, and the hydroxy functional copolymer is present in an amount of from 55 to 99 percent by weight, based on total weight of resin solids.
In another embodiment of the powder thermosetting composition, the functional groups of the copolymer are epoxy functional groups and the reactant is a carboxylic functional reactant having from 4 to 20 carbon atoms. The carboxylic acid reactant is typically one or more of dodecanedioic acid, azelaic acid, adipic acid, 1,6-hexanedioic acid, succinic acid, pimelic acid, sebacic acid, maleic acid, citric acid, itaconic acid, and aconitic acid.
In a further embodiment of the powder thermosetting composition, the functional groups of the copolymer are carboxylic functional groups and the reactant is a beta-hydroxyalkylamide. In this embodiment, the powder thermosetting composition may further include a second polycarboxylic acid, typically one or more of C4 to C20 aliphatic carboxylic acids, polymeric polyanhydrides, polyesters, polyurethanes, and mixtures thereof. The beta-hydroxyalkylamide is typically one represented by structure IX as detailed above.
The powder thermosetting composition of the present invention may also include one or more cure catalysts for catalyzing the reaction between the crosslinking agent and the functional copolymer. Classes of useful catalysts include metal compounds, in particular, organic tin compounds, and tertiary amines. Examples of organic tin compounds include, but are not limited to, tin(II) salts of carboxylic acids, e.g., tin(II) acetate, tin(II) octanoate, tin(II) ethylhexanoate and tin(II) laurate; tin(IV) compounds, e.g., dibutyltin oxide, dibutyltin dichloride, dibutyltin diacetate, dibutyltin dilaurate, dibutyltin maleate, and dioctyltin diacetate. Examples of suitable tertiary amine catalysts include, but are not limited to, diazabicyclo[2.2.2]octane and 1,5-diazabicyclo[4,3,0]non-5-ene. Preferred catalysts include tin(II) octanoate and dibutyltin(IV) dilaurate.
The powder thermosetting composition of the present invention may also include pigments and fillers. Examples of pigments include, but are not limited to, inorganic pigments, e.g., titanium dioxide and iron oxides, organic pigments, e.g., phthalocyanines, anthraquinones, quinacridones and thioindigos, and carbon blacks. Examples of fillers include, but are not limited to, silica, e.g., precipitated silicas, clay, and barium sulfate. When used in the composition of the present invention, pigments and fillers are typically present in amounts of from 0.1 percent to 70 percent by weight, based on total weight of the thermosetting composition. More often, the thermosetting composition of the present invention is used as a clear composition being substantially free of pigments and fillers.
The powder thermosetting composition of the present invention may optionally contain additives such as waxes for flow and wetting, flow control agents, e.g., poly(2-ethylhexyl)acrylate, degassing additives such as benzoin, adjuvant resin to modify and optimize coating properties, antioxidants and ultraviolet (UV) light absorbers. Examples of useful antioxidants and UV light absorbers include those available commercially from Ciba-Geigy under the trademarks IRGANOX and TINUVIN. These optional additives, when used, are typically present in amounts up to 20 percent by weight, based on total weight of the thermosetting composition.
The powder thermosetting composition of the present invention is typically prepared by first dry blending the hydroxy functional polymer, the crosslinking agent and additives, such as flow control agents, degassing agents and catalysts, in a blender, e.g., a Henshel blade blender. The blender is operated for a period of time sufficient to result in a homogenous dry blend of the materials charged thereto. The homogenous dry blend is then melt blended in an extruder, e.g., a twin screw co-rotating extruder, operated within a temperature range of 80xc2x0 C. to 140xc2x0 C., e.g., from 100xc2x0 C. to 125xc2x0 C. The extrudate of the thermosetting composition of the present invention is cooled and, when used as a powder coating composition, is typically milled to an average particle size of from, for example, 15 to 30 microns.
In a particular embodiment of the present invention, the thermosetting composition is a thermosetting composition that includes a resinous phase dispersed in an aqueous medium. The resinous phase includes an ungelled copolymer composition that includes the copolymer composition described above having a functional group containing one or more active hydrogen groups and a suitable ionic group; and a curing agent having at least two functional groups that are reactive with the active hydrogen groups of the copolymer. Suitable ionic groups include anionic groups and cationic groups. A non-limiting example of a suitable cationic group is an onium salt group. The active hydrogen group-containing copolymer typically has a number average molecular weight in the range of from 1,000 to 30,000.
The functional copolymer has an equivalent weight of from 100 to 5,000 grams/equivalent and the equivalent ratio of functional groups in the curing agent to equivalents in the functional copolymer is within the range of 1:3 to 3:1. The curing agent is present in an amount of from 1 to 45 percent by weight, based on total weight of resin solids, and the functional copolymer is present in an amount of from 55 to 99 percent by weight, based on total weight of resin solids.
The thermosetting composition is in the form of an aqueous dispersion. The term xe2x80x9cdispersionxe2x80x9d is believed to be a two-phase transparent, translucent, or opaque resinous system in which the resin is in the dispersed phase and the water is in the continuous phase. The average particle size of the resinous phase is generally less than 1.0 and usually less than 0.5 microns, preferably less than 0.15 micron.
The concentration of the resinous phase in the aqueous medium is at least 1 and usually from about 2 to about 60 percent by weight based on total weight of the aqueous dispersion. When the compositions of the present invention are in the form of resin concentrates, they generally have a resin solids content of about 20 to about 60 percent by weight based on weight of the aqueous dispersion.
The active hydrogen groups of the copolymer are typically provided by residues of one or more of the monomers hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, acrylic acid, methacrylic acid, acrylamide, methacrylamide, 2-carbamoyloxyethyl acrylate, 2-carbamoyloxyethyl methacrylate, 2-carbamoyloxypropryl acrylate and 2-carbamyloyloxypropryl methacrylate. More specifically, the active hydrogen groups in the copolymer may be one or more of carboxylic acid, hydroxy, amide, and carbamate; and functional groups of the curing agent are different than those in the copolymer and are one or more of epoxy or oxirane, carboxylic acid, hydroxy, polyol, isocyanate, capped isocyanate, amine, aminoplast, and beta-hydroxyalkylamide.
The onium salt functional monomers are typically one or more of quaternary ammonium salts and ternary sulfonium salts. Non-limiting examples of onium salt functional monomers, residues of which may be included in the present functional copolymer include an epoxy group-containing ethylenically unsaturated monomer which after polymerization has been post-reacted with an amine acid salt, an amine acid salt of dimethyl aminoethyl acrylate, or dimethyl aminoethyl methacrylate and at least one epoxy group-containing monomer which after polymerization has been post-reacted with a sulfide in the presence of an acid. The curing agent is present in an amount of from 1 to 75, in some cases 1 to 45, and typically 1 to 25 percent by weight, based on total weight of resin solids, and the functional copolymer is present in an amount of from 25 to 99, in some cases 55 to 99, and typically 75 to 99 percent by weight, based on total weight of resin solids.
The thermosetting composition is in the form of an aqueous dispersion of the invention and typically in the form of electrodeposition baths which are usually supplied as two components: (1) a clear resin feed, which includes generally the active hydrogen-containing polymer which contains onium salt groups, i.e., the main film-forming polymer, the curing agent, and any additional water-dispersible, non-pigmented components; and (2) a pigment paste, which generally includes one or more pigments, a water-dispersible grind resin which can be the same or different from the main-film forming polymer, and, optionally, additives such as wetting or dispersing aids. Electrodeposition bath components (1) and (2) are dispersed in an aqueous medium which comprises water and, usually, coalescing solvents. Alternatively, the electrodeposition bath may be supplied as a one-component system which contains the main film-forming polymer, the curing agent, the pigment paste, and any optional additives in one package. The one-component system is dispersed in an aqueous medium as described above.
The electrodeposition bath of the present invention has a resin solids content usually within the range of about 5 to 25 percent by weight based on total weight of the electrodeposition bath.
In addition to water, the aqueous medium may contain a coalescing solvent. Useful coalescing solvents include hydrocarbons, alcohols, esters, ethers, and ketones. The preferred coalescing solvents include alcohols, polyols, and ketones. Specific coalescing solvents include isopropanol, butanol, 2-ethylhexanol, isophorone, 2-methoxypentanone, ethylene, and propylene glycol and the monoethyl, monobutyl, and monohexyl ethers of ethylene or propylene glycol. The amount of coalescing solvent is generally between about 0.01 and 25 percent and, when used, preferably from about 0.05 to about 5 percent by weight based on total weight of the aqueous medium.
A pigment composition and, if desired, various additives, such as surfactants, wetting agents, or catalyst, can be included in the dispersion. The pigment composition may be of the conventional type comprising pigments, for example, iron oxides, strontium chromate, carbon black, coal dust, titanium dioxide, talc, barium sulfate, as well as color pigments, such as cadmium yellow, cadmium red, chromium yellow, and the like. The pigment content of the dispersion is usually expressed as a pigment-to-resin ratio. In the practice of the invention, when pigment is employed, the pigment-to-resin ratio is usually within the range of about 0.02 to 1:1. The other additives mentioned above are usually in the dispersion in amounts of about 0.01 to 3 percent by weight based on weight of resin solids.
In an embodiment of the resinous phase dispersed in an aqueous medium, the active hydrogen functional groups of copolymer are hydroxy and the functional groups of the curing agent are a capped polyisocyanate. The capping group of the capped polyisocyanate crosslinking agent is one or more of hydroxy functional compounds, 1H-azoles, lactams, and ketoximes. The capping group is one or more of phenol, p-hydroxy methylbenzoate, 1H-1,2,4-triazole, 1H-2,5-dimethyl pyrazole, 2-propanone oxime, 2-butanone oxime, cyclohexanone oxime, and e-caprolactam. The polyisocyanate of the capped polyisocyanate curing agent is one or more of of 1,6-hexamethylene diisocyanate, cyclohexane diisocyanate, xcex1,xcex1xe2x80x2-xylylene diisocyanate, xcex1,xcex1,xcex1xe2x80x2,xcex1xe2x80x2-tetramethylxylylene diisocyanate, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane, diisocyanato-dicyclohexylmethane, dimers of said polyisocyanates, and trimers of the polyisocyanates.
In a particular embodiment of the thermosetting composition having a resinous phase dispersed in an aqueous medium, the functional groups of copolymer are carboxylic acid functional groups and the curing agent is a beta-hydroxyalkylamide compound. The thermosetting composition may further include a second polycarboxylic acid functional material, which may be one or more of C4 to C20 aliphatic carboxylic acids, polymeric polyanhydrides, polyesters, and polyurethanes. The beta-hydroxyalkylamide is typically one represented by structure VIII as detailed above.
In a specific embodiment of the thermosetting composition having a resinous phase dispersed in an aqueous medium, the copolymer is a substantially linear polymer having a number average molecular weight in the range of from 1,000 to 30,000. The copolymer includes residues from an onium salt functional monomer derived from at least one epoxy group-containing monomer which, after polymerization, has been post-reacted with an amine acid salt, hydroxy alkyl acrylates, or methacrylates having 1 to 4 carbon atoms in the alkyl group, at least one acrylate acceptor monomer, and a monomer decribed by structure I.
The present invention is also directed to a method of coating a substrate, which includes the steps of:
(A) applying a thermosetting composition to the substrate;
(B) coalescing the thermosetting composition to form a substantially continuous film; and
(C) curing the thermosetting composition.
The thermosetting composition is typically the liquid thermosetting composition or powder thermosetting composition described above. The thermosetting composition includes the copolymer composition of the present invention, which includes a functional copolymer as previously described and a crosslinking agent having at least two functional groups that are reactive with the functional groups of the functional copolymer.
The thermosetting compositions described above can be applied to various substrates to which they adhere, including wood; metals such as ferrous substrates and aluminum substrates; glass; plastic, plastic and sheet molding compound based plastics.
The compositions can be applied by conventional means including brushing, dipping, flow coating, spraying, and the like, but they are most often applied by spraying. The usual spray techniques and equipment for air spraying and electrostatic spraying and either manual or automatic methods can be used. Substrates that may be coated by the method of the present invention include, for example, wood, metal, glass, and plastic.
The thermosetting composition of the present invention may be applied to the substrate by any appropriate means that are known to those of ordinary skill in the art. The thermosetting composition may be in the form of a dry powder or, alternatively, a liquid medium. When the substrate is electrically conductive, the thermosetting composition is typically electrostatically applied. Electrostatic spray application generally involves drawing the thermosetting composition from a fluidized bed and propelling it through a corona field. The particles of the thermosetting composition become charged as they pass through the corona field and are attracted to and deposited upon the electrically conductive substrate, which is grounded. As the charged particles begin to build up, the substrate becomes insulated, thus limiting further particle deposition. This insulating phenomenon typically limits the film build of the deposited composition to a maximum of 3 to 6 mils (75 to 150 microns).
Alternatively, when the substrate is not electrically conductive, for example as is the case with many plastic substrates, the substrate is typically preheated prior to application of the thermosetting composition. The preheated temperature of the substrate is equal to or greater than that of the melting point of the thermosetting composition, but less than its cure temperature. With spray application over preheated substrates, film builds of the thermosetting composition in excess of 6 mils (150 microns) can be achieved, e.g., 10 to 20 mils (254 to 508 microns).
When the thermosetting composition is a liquid, the composition is allowed to coalesce to form a substantially continuous film on the substrate. Typically, the film thickness will be about 0.01 to about 5 mils (about 0.254 to about 127 microns), preferably about 0.1 to about 2 mils (about 2.54 to about 50.8 microns) in thickness. The film is formed on the surface of the substrate by driving solvent, i.e., organic solvent and/or water, out of the film by heating or by an air drying period. Preferably, the heating will only be for a short period of time, sufficient to ensure that any subsequently applied coatings can be applied to the film without dissolving the composition. Suitable drying conditions will depend on the particular composition but, in general, a drying time of from about 1 to 5 minutes at a temperature of about 68-250xc2x0 F. (20-121xc2x0 C.) will be adequate. More than one coat of the composition may be applied to develop the optimum appearance. Between coats, the previously applied coat may be flashed, that is, exposed to ambient conditions for about 1 to 20 minutes.
After application to the substrate, the thermosetting composition is then coalesced to form a substantially continuous film. Coalescing of the applied composition is generally achieved through the application of heat at a temperature equal to or greater than that of the melting point of the composition, but less than its cure temperature. In the case of preheated substrates, the application and coalescing steps can be achieved in essentially one step.
The coalesced thermosetting composition is next cured by the application of heat. As used herein and in the claims, by xe2x80x9ccuredxe2x80x9d is meant a three dimensional crosslink network formed by covalent bond formation, e.g., between the free isocyanate groups of the crosslinking agent and the hydroxy groups of the polymer. The temperature at which the thermosetting composition of the present invention cures is variable and depends in part on the type and amount of catalyst used. Typically, the thermosetting composition has a cure temperature within the range of 130xc2x0 C. to 160xc2x0 C., e.g., from 140xc2x0 C. to 150xc2x0 C.
In accordance with the present invention, there is further provided a multi-component composite coating composition that includes a base coat deposited from a pigmented film-forming composition; and a transparent top coat applied over the base coat. Either the base coat or the transparent top coat or both coats may include the liquid thermosetting composition or the powder thermosetting composition described above. The multi-component composite coating composition as described herein is commonly referred to as a color-plus-clear coating composition.
The pigmented film-forming composition from which the base coat is deposited can be any of the compositions useful in coatings applications, particularly automotive applications in which color-plus-clear coating compositions are extensively used. Pigmented film-forming compositions conventionally comprise a resinous binder and a pigment to act as a colorant. Particularly useful resinous binders are acrylic polymers, polyesters including alkyds, polyurethanes, and the copolymer composition of the present invention.
The resinous binders for the pigmented film-forming base coat composition can be organic solvent-based materials, such as those described in U.S. Pat. No. 4,220,679, note column 2, line 24 through column 4, line 40. Also, water-based coating compositions such as those described in U.S. Pat. Nos. 4,403,003, 4,147,679, and 5,071,904 can be used as the binder in the pigmented film-forming composition.
The pigmented film-forming base coat composition is colored and may also contain metallic pigments. Examples of suitable pigments can be found in U.S. Pat. Nos. 4,220,679, 4,403,003, 4,147,679, and 5,071,904.
Ingredients that may be optionally present in the pigmented film-forming base coat composition are those which are well known in the art of formulating surface coatings and include surfactants, flow control agents, thixotropic agents, fillers, anti-gassing agents, organic co-solvents, catalysts, and other customary auxiliaries. Examples of these optional materials and suitable amounts are described in the aforementioned U.S. Pat. Nos. 4,220,679, 4,403,003, 4,147,769, and 5,071,904.
The pigmented film-forming base coat composition can be applied to the substrate by any of the conventional coating techniques, such as brushing, spraying, dipping, or flowing, but are most often applied by spraying. The usual spray techniques and equipment for air spraying, airless spray, and electrostatic spraying employing either manual or automatic methods can be used. The pigmented film-forming composition is applied in an amount sufficient to provide a base coat having a film thickness typically of 0.1 to 5 mils (2.5 to 125 microns) and preferably 0.1 to 2 mils (2.5 to 50 microns).
After deposition of the pigmented film-forming base coat composition onto the substrate, and prior to application of the transparent top coat, the base coat can be cured or alternatively dried. In drying the deposited base coat, organic solvent and/or water is driven out of the base coat film by heating or the passage of air over its surface. Suitable drying conditions will depend on the particular base coat composition used and on the ambient humidity in the case of certain water-based compositions. In general, drying of the deposited base coat is performed over a period of from 1 to 15 minutes and at a temperature of 21xc2x0 C. to 93xc2x0 C.
The transparent top coat is applied over the deposited base coat by any of the methods by which coatings are known to be applied. In an embodiment of the present invention, the transparent top coat is applied by electrostatic spray application as described previously herein. When the transparent top coat is applied over a deposited base coat that has been dried, the two coatings can be co-cured to form the multi-component composite coating composition of the present invention. Both the base coat and top coat are heated together to conjointly cure the two layers. Typically, curing conditions of 130xc2x0 C. to 160xc2x0 C. for a period of 20 to 30 minutes are employed. The transparent top coat typically has a thickness within the range of 0.5 to 6 mils (13 to 150 microns), e.g., from 1 to 3 mils (25 to 75 microns).
In an embodiment of the present invention, the present thermosetting composition having a resinous phase dispersed in an aqueous medium may be an electrocoating composition used to electrocoat a conductive substrate. In such an instance, the present invention is directed to a method of electrocoating a conductive substrate serving as a cathode in an electrical circuit comprising the cathode and an anode. The cathode and anode are immersed in the aqueous electrocoating composition, and an electric current is passed between the cathode and the anode to cause deposition of the electrocoating composition on the substrate as a substantially continuous film. The aqueous electrocoating composition is the resinous phase of the thermosetting composition having a resinous phase dispersed in an aqueous medium.
Further to this embodiment, the active hydrogen group-containing copolymer containing an ionic group, such as an onium salt groups may be present in the thermosetting compositions of the invention as a resinous binder (i.e., a film-forming polymer) or as an additive in combination with a separate resinous binder. When used as an additive, for example, as a reactive diluent, the active hydrogen group-containing polymer as described herein typically has a high degree of functionality and a correspondingly low equivalent weight. However, it should be appreciated that for other applications, the additive may have low functionality (it may be monofunctional) and a correspondingly high equivalent weight.
The active hydrogen group-containing polymer containing ionic groups is typically present in the thermosetting compositions of the invention in an amount of at least 0.5 percent by weight (when used as an additive) and in an amount of at least 25 percent by weight (when used as a resinous binder), based on total weight of resin solids of the thermosetting composition. The active hydrogen group-containing polymers are also typically present in the thermosetting compositions in an amount of less than 95 percent by weight, and preferably in an amount of less than 80 percent by weight, based on total weight of resin solids of the thermosetting composition. The active hydrogen group-containing polymer may be present in the thermosetting compositions of the invention in an amount ranging between any combination of these values, inclusive of the recited values.
The thermosetting compositions of the invention are typically in the form of electrodeposition baths which are usually supplied as two components: (1) a clear resin feed, which includes generally the active hydrogen-containing polymer which contains onium salt groups, i.e., the main film-forming polymer, the curing agent, and any additional water-dispersible, non-pigmented components; and (2) a pigment paste, which generally includes one or more pigments, a water-dispersible grind resin which can be the same or different from the main-film forming polymer, and, optionally, additives, such as wetting or dispersing aids. Electrodeposition bath components (1) and (2) are dispersed in an aqueous medium which comprises water and, usually, coalescing solvents. Alternatively, the electrodeposition bath may be supplied as a one-component system which contains the main film-forming polymer, the curing agent, the pigment paste, and any optional additives in one package. The one-component system is dispersed in an aqueous medium as described above.
The electrodeposition bath of the present invention has a resin solids content usually within the range of about 5 to 25 percent by weight based on total weight of the electrodeposition bath.
As aforementioned, besides water, the aqueous medium may contain a coalescing solvent. Useful coalescing solvents include hydrocarbons, alcohols, esters, ethers, and ketones. The preferred coalescing solvents include alcohols, polyols and ketones. Specific coalescing solvents include isopropanol, butanol, 2-ethylhexanol, isophorone, 2-methoxypentanone, ethylene, and propylene glycol and the monoethyl, monobutyl, and monohexyl ethers of ethylene or propylene glycol. The amount of coalescing solvent is generally between about 0.01 and 25 percent and, when used, preferably from about 0.05 to about 5 percent by weight based on total weight of the aqueous medium.
As discussed above, a pigment composition and, if desired, various additives, such as surfactants, wetting agents, or catalyst, can be included in the dispersion. The pigment composition may be of the conventional type comprising pigments, for example, iron oxides, strontium chromate, carbon black, coal dust, titanium dioxide, talc, barium sulfate, as well as color pigments, such as cadmium yellow, cadmium red, chromium yellow, and the like. The pigment content of the dispersion is usually expressed as a pigment-to-resin ratio. In the practice of the invention, when pigment is employed, the pigment-to-resin ratio is usually within the range of about 0.02 to 1:1. The other additives mentioned above are usually in the dispersion in amounts of about 0.01 to 3 percent by weight based on weight of resin solids.
The thermosetting compositions of the present invention can be applied by electrodeposition to a variety of electroconductive substrates, especially metals, such as untreated steel, galvanized steel, aluminum, copper, magnesium, and conductive carbon-coated materials. The applied voltage for electrodeposition may be varied and can be, for example, as low as 1 volt to as high as several thousand volts, but typically between 50 and 500 volts. The current density is usually between 0.5 ampere and 5 amperes per square foot and tends to decrease during electrodeposition indicating the formation of an insulating film.
After the coating has been applied by electrodeposition, it is cured usually by baking at elevated temperatures, such as about 90xc2x0 to about 260xc2x0 C. for about 1 to about 40 minutes.
The present invention further provides a primed multi-component composite coating composition that includes a primer coat applied by electrodeposition; a base coat deposited from a pigmented film-forming composition; and optionally a transparent top coat applied over the base coat. The electrodeposited primer may include an aqueous electrocoating composition that includes a resinous phase including the present thermosetting composition for electrodeposition described above. The base coat and/or the transparent top coat may include the liquid thermosetting composition or the powder thermosetting composition described above.
Typically, A primer coat is deposited via electrodeposition as described above and cured as described above. Subsequently, a pigmented film-forming base coat composition is applied over the primer coated substrate, and prior to application of a top coat. The base coat can be cured or alternatively dried. In drying the deposited base coat, organic solvent and/or water is driven out of the base coat film by heating or the passage of air over its surface. Suitable drying conditions will depend on the particular base coat composition used and on the ambient humidity in the case of certain water-based compositions. In general, drying of the deposited base coat is performed over a period of from 1 to 15 minutes and at a temperature of 21xc2x0 C. to 93xc2x0 C.
The top coat may be applied over the deposited base coat by any of the methods by which coatings are known to be applied. In an embodiment of the present invention, the top coat is applied by electrostatic spray application as described previously herein. When the top coat is applied over a deposited base coat that has been dried, the two coatings can be co-cured to form the primed multi-component composite coating composition of the present invention. Both the base coat and top coat are heated together to conjointly cure the two layers. Typically, curing conditions of 130xc2x0 C. to 160xc2x0 C. for a period of 20 to 30 minutes are employed. The transparent top coat typically has a thickness within the range of 0.5 to 6 mils (13 to 150 microns), e.g., from 1 to 3 mils (25 to 75 microns).
The present invention is more particularly described in the following examples, which are intended to be illustrative only, since numerous modifications and variations therein will be apparent to those skilled in the art. Unless otherwise specified, all parts and percentages are by weight.
The following abbreviations are used in the examples.